1. Copyright 2006 by Pearson Education 1 Building Java Programs Chapter 5: Program Logic and Indefinite Loops

2. Copyright 2006 by Pearson Education 2 Chapter outline indefinite loops the while loop sentinel loops generating random numbers with Random objects Boolean logic boolean expressions and variables logical operators testing for valid user input indefinite loop variations the do/while loop logical assertions

3. Copyright 2006 by Pearson Education 3 while loops reading: 5.1

4. Copyright 2006 by Pearson Education 4 Definite loops definite loop: One that executes a known number of times. The for loops we have seen so far are definite loops. We often use language like, "Repeat these statements N times." "For each of these 10 things,...." Examples: Print "hello" 10 times. Find all the prime numbers up to an integer n. Print each odd number between 5 and 127.

5. Copyright 2006 by Pearson Education 5 Indefinite loops indefinite loop: One where it is not obvious in advance how many times it will execute. The while loops in this chapter are indefinite loops. We often use language like, "Keep looping as long as or while this condition is still true." "Don't stop looping until the following happens." Examples: Prompt the user until they type a non-negative number. Print random numbers until a prime number is printed. Continue looping while the user has not typed "n" to quit.

6. Copyright 2006 by Pearson Education 6 The while loop statement while loop: Executes as long as a condition is true. well suited to writing indefinite loops while loop, general syntax: while ( ) { ; } Example: int number = 1; while (number <= 200) { System.out.print(number + " "); number = number * 2; } OUTPUT: 1 2 4 8 16 32 64 128

7. Copyright 2006 by Pearson Education 7 While loop flow chart

8. Copyright 2006 by Pearson Education 8 Example while loop Finds and prints a number's first factor other than 1: Scanner console = new Scanner(System.in); System.out.print("Type a number: "); int number = console.nextInt(); int factor = 2; while (number % factor != 0) { factor++; } System.out.println("First factor: " + factor); Example log of execution: Type a number: 91 First factor: 7

9. Copyright 2006 by Pearson Education 9 Equivalence of for,while loops Any for loop of the following form: for ( ; ; ) { ; } can be replaced by a while loop of the following form: ; while ( ) { ; }

10. Copyright 2006 by Pearson Education 10 for/while loop example What while loop is essentially equivalent to the following for loop? for (int i = 1; i <= 10; i++) { System.out.println(i + " squared = " + (i * i)); } ANSWER: int i = 1; while (i <= 10) { System.out.println(i + " squared = " + (i * i)); i++; }

11. Copyright 2006 by Pearson Education 11 While loop question Write a piece of Java code that uses a while loop to repeatedly prompt the user to type a number until the user types a non-negative number, then square it. Example log of execution: Type a non-negative integer: -5 Invalid number, try again: -1 Invalid number, try again: -235 Invalid number, try again: -87 Invalid number, try again: 11 11 squared is 121

12. Copyright 2006 by Pearson Education 12 While loop answer Solution: System.out.print("Type a non-negative integer: "); int number = console.nextInt(); while (number < 0) { System.out.print("Invalid number, try again: "); number = console.nextInt(); } int square = number * number; System.out.println(number + " squared is " + square); Notice that number has to be declared outside the loop in order to remain in scope.

13. Copyright 2006 by Pearson Education 13 While loop question Write a method named digitSum that accepts an integer as a parameter and returns the sum of the digits of that number. digitSum(29107) returns 2+9+1+0+7 or 19 Assume that the number is non-negative. Hint: Use the % operator to extract the last digit of a number. If we do this repeatedly, when should we stop?

14. Copyright 2006 by Pearson Education 14 While loop answer The following code implements the method: public static int digitSum(int n) { int sum = 0; while (n > 0) { sum = sum + (n % 10); // add last digit to sum n = n / 10; // remove last digit } return sum; }

15. Copyright 2006 by Pearson Education 15 Sentinel loops reading: 5.1

16. Copyright 2006 by Pearson Education 16 Sentinel values sentinel: A special input value that signals the end of the user's input. sentinel loop: Repeats until a sentinel value is seen. Example: Write a program that repeatedly prompts the user for numbers to add until the user types 0, then outputs their sum. (In this case, 0 is our sentinel value.) Example log of execution: Enter a number (0 to quit): 95 Enter a number (0 to quit): 87 Enter a number (0 to quit): 42 Enter a number (0 to quit): 26 Enter a number (0 to quit): 0 The total was 250

17. Copyright 2006 by Pearson Education 17 Flawed sentinel solution What's wrong with this solution? Scanner console = new Scanner(System.in); int sum = 0; int inputNumber = 1; // "dummy value", anything but 0 while (inputNumber != 0) { System.out.print("Enter a number (0 to quit): "); inputNumber = console.nextInt(); sum += inputNumber; } System.out.println("The total was " + sum);

18. Copyright 2006 by Pearson Education 18 A different sentinel value Modify your program to use a sentinel value of -1. Example log of execution: Enter a number (-1 to quit): 95 Enter a number (-1 to quit): 87 Enter a number (-1 to quit): 42 Enter a number (-1 to quit): 26 Enter a number (-1 to quit): -1 The total was 250

19. Copyright 2006 by Pearson Education 19 Changing the sentinel value To see the problem, change the sentinel's value to -1: Scanner console = new Scanner(System.in); int sum = 0; int inputNumber = 1; // "dummy value", anything but -1 while (inputNumber != -1) { System.out.print("Enter a number (-1 to quit): "); inputNumber = console.nextInt(); sum += inputNumber; } System.out.println("The total was " + sum); Now the solution produces the wrong output. Why? The total was 249

20. Copyright 2006 by Pearson Education 20 The problem with our code Our code uses a pattern like this: sum = 0. while (input is not the sentinel) { prompt for input; read input. add input to the sum. } On the last pass through the loop, the sentinel value -1 is added to the sum: prompt for input; read input (-1). add input (-1) to the sum. This is a fencepost problem. We want to read N numbers (N is not known ahead of time), but only sum the first N - 1 of them.

21. Copyright 2006 by Pearson Education 21 A fencepost solution We need the code to use a pattern like this: sum = 0. prompt for input; read input. while (input is not the sentinel) { add input to the sum. prompt for input; read input. } Sentinel loops often utilize a fencepost-style "loop-and- a-half" solution by pulling some code out of the loop.

22. Copyright 2006 by Pearson Education 22 Correct code This solution produces the correct output: Scanner console = new Scanner(System.in); int sum = 0; System.out.print("Enter a number (-1 to quit): "); int inputNumber = console.nextInt(); while (inputNumber != -1) { sum += inputNumber; // moved to top of loop System.out.print("Enter a number (-1 to quit): "); inputNumber = console.nextInt(); } System.out.println("The total was " + sum);

23. Copyright 2006 by Pearson Education 23 Constant with sentinel A better solution creates a constant for the sentinel: public static final int SENTINEL = -1; This solution uses the constant: Scanner console = new Scanner(System.in); int sum = 0; System.out.print("Enter a number (" + SENTINEL + " to quit): "); int inputNumber = console.nextInt(); while (inputNumber != SENTINEL) { sum += inputNumber; System.out.print("Enter a number (" + SENTINEL + " to quit): "); inputNumber = console.nextInt(); } System.out.println("The total was " + sum);

24. Copyright 2006 by Pearson Education 24 Generating random numbers reading: 5.1

25. Copyright 2006 by Pearson Education 25 The Random class Random objects generate pseudo-random numbers. Class Random is found in the java.util package. import java.util.*; Example: Random rand = new Random(); int randomNumber = rand.nextInt(10); // randomNumber has a random value between 0 and 9 Method nameDescription nextInt() returns a random integer nextInt( max ) returns a random integer in the range [0, max) in other words, from 0 through one less than max nextDouble() returns a random real number in the range [0.0, 1.0)

26. Copyright 2006 by Pearson Education 26 Generating random numbers Common usage: to get a random number from 1 to N Example: A random integer between 1 and 20, inclusive: int n = rand.nextInt(20) + 1; To get a number in arbitrary range [min, max]: nextInt( ) + where equals - + 1 Example: A random integer between 5 and 10 inclusive: int n = rand.nextInt(6) + 5;

27. Copyright 2006 by Pearson Education 27 Random questions Given the following declaration, how would you get: Random rand = new Random(); A random number between 0 and 100 inclusive? A random number between 1 and 100 inclusive? A random number between 4 and 17 inclusive?

28. Copyright 2006 by Pearson Education 28 Random answers Given the following declaration, how would you get: Random rand = new Random(); A random number between 0 and 100 inclusive? int random1 = rand.nextInt(101); A random number between 1 and 100 inclusive? int random2 = rand.nextInt(100) + 1; A random number between 4 and 17 inclusive? int random3 = rand.nextInt(14) + 4;

29. Copyright 2006 by Pearson Education 29 Random question Write a program that simulates rolling of two six-sided dice until their combined result comes up as 7. Example log of execution: 2 + 4 = 6 3 + 5 = 8 5 + 6 = 11 1 + 1 = 2 4 + 3 = 7 You won after 5 tries!

30. Copyright 2006 by Pearson Education 30 Random answer // Rolls two dice until a sum of 7 is reached. import java.util.*; public class Roll { public static void main(String[] args) { Random rand = new Random(); int sum = 0; int tries = 0; while (sum != 7) { int roll1 = rand.nextInt(6) + 1; int roll2 = rand.nextInt(6) + 1; sum = roll1 + roll2; System.out.println(roll1 + " + " + roll2 + " = " + sum); tries++; } System.out.println("You won after " + tries + " tries!"); }

31. Copyright 2006 by Pearson Education 31 Random/while question Write a multiplication tutor program. Example log of execution: This program helps you practice multiplication by asking you random multiplication questions with numbers ranging from 1 to 20 and counting how many you solve correctly. 14 * 8 = 112 Correct! 5 * 12 = 60 Correct! 8 * 3 = 24 Correct! 5 * 5 = 25 Correct! 20 * 14 = 280 Correct! 19 * 14 = 256 Incorrect; the answer was 266 You solved 5 correctly.

32. Copyright 2006 by Pearson Education 32 Random/while answer // Asks the user to do multiplication problems and scores them. import java.util.*; public class MultTutor { public static void main(String[] args) { introduction(); Scanner console = new Scanner(System.in); Random rand = new Random(); int num1 = 0; int num2 = 0; int guess = 0; int correct = 0; // loop until user gets one wrong while (guess == num1 * num2) { // pick two random numbers between 1 and 20 inclusive num1 = rand.nextInt(20) + 1; num2 = rand.nextInt(20) + 1; System.out.print(num1 + " * " + num2 + " = "); int guess = console.nextInt(); if (guess == num1 * num2) { System.out.println("Correct!"); } else { System.out.println("Incorrect; the answer was " + (num1 * num2)); } System.out.println("You solved " + correct + " correctly."); }

33. Copyright 2006 by Pearson Education 33 Random/while answer 2... public static void introduction() { System.out.println("This program helps you practice multiplication"); System.out.println("by asking you random multiplication questions"); System.out.println("with numbers ranging from 1 to 20"); System.out.println("and counting how many you solve correctly."); System.out.println(); } Consider changing the code to use a class constant for the maximum value of 20.

34. Copyright 2006 by Pearson Education 34 Random text and others Random can be used in text processing. Code to pick a random lowercase letter: char letter = (char) ('a' + rand.nextInt(26)); Code to pick a random character from a string (in this case, a random vowel): String vowels = "aeiou"; char vow = vowels.charAt(rand.nextInt(vowels.length()); Another example: code to pick a random letter representing a base in a DNA strand (A, C, G, or T): String bases = "ACGT"; char base = bases.charAt(rand.nextInt(bases.length());

35. Copyright 2006 by Pearson Education 35 Other random values Random can be used with double nextDouble method returns a double between 0.0 and 1.0 To get a double in a different range, multiply and/or add Example: Gets a random value between 1.5 and 4.0: double randomGpa = rand.nextDouble() * 2.5 + 1.0; Random can be used to pick between arbitrary choices Code to pick a red, green, or blue color: int r = rand.nextInt(3); if (r == 0) { g.setColor(Color.RED); } else if (r == 1) { g.setColor(Color.GREEN); } else { g.setColor(Color.BLUE); }

36. Copyright 2006 by Pearson Education 36 Boolean logic reading: 5.2

37. Copyright 2006 by Pearson Education 37 Type boolean boolean : A primitive type to represent logical values. A boolean expression produces either true or false. The s in if statements, for loops are boolean. Examples: boolean minor = (age < 21); boolean expensive = (iPhonePrice > 500.00); boolean iLoveCS = true; if (minor) { System.out.println("Can't purchase alcohol!"); } You can create boolean variables, pass boolean parameters, return boolean values from methods,...

38. Copyright 2006 by Pearson Education 38 Methods that return boolean There are methods in Java that return boolean values. A call to one of these methods can be used as a in a for loop, while loop, or if statement. Examples: Scanner console = new Scanner(System.in); System.out.print("Type your name: "); String line = console.nextLine(); if (line.startsWith("Dr.")) { System.out.println("Will you marry me?"); } else if (line.endsWith(", Esq.")) { System.out.println("And I am Ted 'Theodore' Logan!"); }

39. Copyright 2006 by Pearson Education 39 String boolean methods The following String methods return boolean values: MethodDescription equals(String) whether two strings contain exactly the same characters equalsIgnoreCase(String) whether two strings contain the same characters, ignoring upper vs. lower case differences startsWith(String) whether one string contains the other's characters at its start endsWith(String) whether one string contains the other's characters at its end

40. Copyright 2006 by Pearson Education 40 Writing boolean methods Methods can return a boolean result. public static boolean bothOdd(int n1, int n2) { if (n1 % 2 != 0 && n2 % 2 != 0) { return true; } else { return false; } Calls to such methods can be used as conditions: if (bothOdd(7, 13)) {... }

41. Copyright 2006 by Pearson Education 41 Writing boolean methods 2 Another example that returns a boolean result: public static boolean isLowerCaseLetter(char ch) { if ('a' <= ch && ch <= 'z') { return true; } else { return false; } Example call to this method: String name = "e.e. cummings"; char firstLetter = name.charAt(0); if (isLowerCaseLetter(firstLetter)) { System.out.println("You forgot to capitalize your name!"); }

42. Copyright 2006 by Pearson Education 42 "Boolean Zen" Methods that return a boolean result often have an if/else statement: public static boolean bothOdd(int n1, int n2) { if (n1 % 2 != 0 && n2 % 2 != 0) { return true; } else { return false; }... but the if/else is sometimes unnecessary. The if/else 's condition is itself a boolean expression; its value is exactly what you want to return. So do that! public static boolean bothOdd(int n1, int n2) { return (n1 % 2 != 0 && n2 % 2 != 0); }

43. Copyright 2006 by Pearson Education 43 "Boolean Zen" template Replace: public static boolean ( ) { if ( ) { return true; } else { return false; } with: public static boolean ( ) { return ; }

44. Copyright 2006 by Pearson Education 44 Boolean practice problems Write a method named isVowel that returns whether a particular character is a vowel (a, e, i, o, or u). Count only lowercase vowels. isVowel('q') returns false isVowel('e') returns true Write a method named allDigitsOdd that returns whether every digit of a positive integer is odd. allDigitsOdd(19351) returns true allDigitsOdd(234) returns false Write a method named countVowels that returns the number of lowercase vowels in a String. countVowels("zelda") returns 2 countVowels("E Pluribus Unum") returns 4

45. Copyright 2006 by Pearson Education 45 Boolean practice solutions public static boolean isVowel(char c) { if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u') { return true; } else { return false; } or: public static boolean isVowel(char c) { return (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u'); } public static boolean allDigitsOdd(int n) { while (n > 0) { if (n % 2 == 0) { return false; } n /= 2; } return true; }

46. Copyright 2006 by Pearson Education 46 Boolean practice solutions public static int countVowels(String s) { int count = 0; for (int i = 0; i < s.length(); i++) { char c = s.charAt(i); if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u') { count++; } return count; } or: public static int countVowels(String s) { int count = 0; for (int i = 0; i < s.length(); i++) { if (isVowel(s.charAt(i))) { count++; } return count; }

47. Copyright 2006 by Pearson Education 47 Boolean question Modify your previous multiplication tutor program to use a static method that returns a boolean value. This program helps you practice multiplication by asking you random multiplication questions with numbers ranging from 1 to 20 and counting how many you solve correctly. 14 * 8 = 112 Correct! 5 * 12 = 60 Correct! 8 * 3 = 24 Correct! 5 * 5 = 25 Correct! 20 * 14 = 280 Correct! 19 * 14 = 256 Incorrect; the answer was 266 You solved 5 correctly.

48. Copyright 2006 by Pearson Education 48 Boolean answer import java.util.*; // Asks the user to do multiplication problems and scores them. public class MultTutor { public static void main(String[] args) { introduction(); Scanner console = new Scanner(System.in); Random rand = new Random(); // loop until user gets one wrong int correct = 0; while (askQuestion(console, rand)) { correct++; } System.out.println("You solved " + correct + " correctly."); } public static void introduction() { System.out.println("This program helps you practice multiplication"); System.out.println("by asking you random multiplication questions"); System.out.println("with numbers ranging from 1 to 20"); System.out.println("and counting how many you solve correctly."); System.out.println(); }...

49. Copyright 2006 by Pearson Education 49 Boolean answer 2... public static boolean askQuestion(Scanner console, Random rand) { // pick two random numbers between 1 and 20 inclusive int num1 = rand.nextInt(20) + 1; int num2 = rand.nextInt(20) + 1; System.out.print(num1 + " * " + num2 + " = "); int guess = console.nextInt(); if (guess == num1 * num2) { System.out.println("Correct!"); return true; } else { System.out.println("Incorrect; the correct answer was " + (num1 * num2)); return false; }

50. Copyright 2006 by Pearson Education 50 Boolean practice problem Write a program that compares two words typed by the user to see whether they "rhyme" (end with the same last two letters) and/or alliterate (begin with the same letter). Use methods with return values to tell whether two words rhyme and/or alliterate. Example logs of execution: (run #1) Type two words: car STAR They rhyme! (run #2) Type two words: bare bear They alliterate! (run #3) Type two words: sell shell They alliterate! They rhyme!

51. Copyright 2006 by Pearson Education 51 Boolean practice solution // Determines whether two words rhyme and/or start with the same letter. import java.util.*; public class Rhyme { public static void main(String[] args) { Scanner console = new Scanner(System.in); System.out.print("Type two words: "); String word1 = console.next(); String word2 = console.next(); if (rhyme(word1, word2)) { System.out.println("They rhyme!"); } if (alliterate(word1, word2)) { System.out.println("They alliterate!"); } // Returns true if s1 and s2 end with the same two letters. public static boolean rhyme(String s1, String s2) { String endOfWord2 = s2.substring(s2.length() - 2); return s1.endsWith(endOfWord2); } // Returns true if s1 and s2 start with the same letter. public static boolean alliterate(String s1, String s2) { return s1.startsWith(s2.substring(0, 1)); }

52. Copyright 2006 by Pearson Education 52 Boolean practice problem Write a program that prompts for a number and tells whether it is prime, and if not, prints the next prime. Example logs of execution: (run #1) Type a number: 29 29 is prime (run #2) Type two numbers: 14 14 is not prime; the next prime after 14 is 17 As part of your solution, write two methods: isPrime : Returns true if the parameter passed is a prime number nextPrime : Returns the next prime number whose value is greater than or equal to the parameter passed. (If the parameter passed is prime, returns that number.)

53. Copyright 2006 by Pearson Education 53 Boolean practice problem Modify your previous program so that it reads two numbers and tells whether each is prime, or if not, gives the next prime after them. Also report whether the two numbers are relatively prime (have no common factors). Example logs of execution: (run #1) Type two numbers: 9 16 9 is not prime; the next prime after 9 is 11 16 is not prime; the next prime after 16 is 17 9 and 16 are relatively prime (run #2) Type two numbers: 7 21 7 is prime 21 is not prime; the next prime after 21 is 23 7 and 21 are not relatively prime

54. Copyright 2006 by Pearson Education 54 Boolean practice solution import java.util.*; public class Primes { public static void main(String[] args) { Scanner console = new Scanner(System.in); System.out.print("Type two numbers: "); int num1 = console.nextInt(); int num2 = console.nextInt(); primeTest(num1); primeTest(num2); if (relativelyPrime(num1, num2)) { System.out.println(num1 + " and " + num2 + " are relatively prime"); } else { System.out.println(num1 + " and " + num2 + " are not relatively prime"); } public static void primeTest(int number) { if (isPrime(number)) { System.out.println(number + " is prime"); } else { System.out.println("the next prime after " + number + " is " + nextPrime(number)); } public static boolean isPrime(int number) { return countFactors(number) <= 2; }...

55. Copyright 2006 by Pearson Education 55 Boolean practice solution 2... public static int nextPrime(int number) { while (countFactors(number) > 2) { number++; } return number; // number is now prime } public static int countFactors(int number) { int count = 1; for (int i = 2; i <= number; i++) { if (number % i == 0) { count++; // i is a factor } return count; } public static boolean relativelyPrime(int n1, int n2) { return commonFactors(n1, n2) == 1; } // Returns the number of public static int commonFactors(int n1, int n2) { int count = 1; for (int i = 2; i <= Math.min(n1, n2); i++) { if (n1 % i == 0 && n2 % i == 0) { count++; // i is a common factor } return count; }

56. Copyright 2006 by Pearson Education 56 Indefinite loop variations reading: 5.4

57. Copyright 2006 by Pearson Education 57 The do/while loop do/while loop: Executes statements repeatedly while a condition is true, testing it at the end of each repetition. Similar to a while loop, except that its body statement(s) will always execute the first time, regardless of whether the condition is true or false. The do/while loop, general syntax: do { ; } while ( ); Example: // roll until we get a number other than 3 Random rand = new Random(); int dice; do { dice = rand.nextInt(); } while (dice == 3);

58. Copyright 2006 by Pearson Education 58 do/while loop flow chart

59. Copyright 2006 by Pearson Education 59 do/while question Modify the previous dice program to use a do/while loop. Example log of execution: 2 + 4 = 6 3 + 5 = 8 5 + 6 = 11 1 + 1 = 2 4 + 3 = 7 You won after 5 tries!

60. Copyright 2006 by Pearson Education 60 do/while solution // Rolls two dice until a sum of 7 is reached. import java.util.*; public class Roll { public static void main(String[] args) { Random rand = new Random(); int tries = 0; int sum; do { int roll1 = rand.nextInt(6) + 1; int roll2 = rand.nextInt(6) + 1; sum = roll1 + roll2; System.out.println(roll1 + " + " + roll2 + " = " + sum); tries++; } while (sum != 7); System.out.println("You won after " + tries + " tries!"); }

61. Copyright 2006 by Pearson Education 61 "Forever" loop with break break statement: Immediately exits a loop. Can be used to write a loop whose test is in the middle. Such loops are often called "forever" loops because their header's boolean test is often changed to a trivial true. "forever" loop, general syntax: while (true) { ; if ( ) { break; } ; }

62. Copyright 2006 by Pearson Education 62 Sentinel loop with break A working sentinel loop solution using break : Scanner console = new Scanner(System.in); int sum = 0; while (true) { System.out.print("Enter a number (-1 to quit): "); int inputNumber = console.nextInt(); if (inputNumber == -1) { // don't add -1 to sum break; } sum += inputNumber; // inputNumber != -1 here } System.out.println("The total was " + sum);

63. Copyright 2006 by Pearson Education 63Assertions reading: 5.5

64. Copyright 2006 by Pearson Education 64 Logical assertions assertion: A statement that is either true or false. Examples: Java was created in 1995. The sky is purple. 23 is a prime number. 10 is greater than 20. x divided by 2 equals 7. (depends on the value of x)

65. Copyright 2006 by Pearson Education 65 Assertions in code We can make assertions about our code and ask whether they are true at various points in the code. Valid answers are ALWAYS, NEVER, or SOMETIMES. System.out.print("Type a nonnegative number: "); double number = console.nextDouble(); // Point A: is number < 0.0 here? while (number < 0.0) { // Point B: is number < 0.0 here? System.out.print("Negative; try again: "); number = console.nextDouble(); // Point C: is number < 0.0 here? } // Point D: is number < 0.0 here? We can make assertions about our code and ask whether they are true at various points in the code. Valid answers are ALWAYS, NEVER, or SOMETIMES. System.out.print("Type a nonnegative number: "); double number = console.nextDouble(); // Point A: is number < 0.0 here? (SOMETIMES) while (number < 0.0) { // Point B: is number < 0.0 here? (ALWAYS) System.out.print("Negative; try again: "); number = console.nextDouble(); // Point C: is number < 0.0 here? (SOMETIMES) } // Point D: is number < 0.0 here? (NEVER)

66. Copyright 2006 by Pearson Education 66 Assertion example 1 public static int mystery(Scanner console) { int prev = 0; int count = 0; int next = console.nextInt(); // Point A while (next != 0) { // Point B if (next == prev) { // Point C count++; } prev = next; next = console.nextInt(); // Point D } // Point E return count; } next == 0prev == 0next == prev Point A Point B Point C Point D Point E Which of the following assertions are true at which point(s) in the code? Choose ALWAYS, NEVER, or SOMETIMES. next == 0prev == 0next == prev Point A SOMETIMESALWAYSSOMETIMES Point B NEVERSOMETIMES Point C NEVER ALWAYS Point D SOMETIMESNEVERSOMETIMES Point E ALWAYSSOMETIMES

67. Copyright 2006 by Pearson Education 67 Assertion example 2 public static void mystery(int x, int y) { int z = 0; // Point A while (x >= y) { // Point B x -= y; // Point C z++; // Point D } // Point E System.out.println( z + " " + x); } x < yx == yz == 0 Point A Point B Point C Point D Point E Which of the following assertions are true at which point(s) in the code? Choose ALWAYS, NEVER, or SOMETIMES. x < yx == yz == 0 Point A SOMETIMES ALWAYS Point B NEVERSOMETIMES Point C SOMETIMES Point D SOMETIMES NEVER Point E ALWAYSNEVERSOMETIMES

68. Copyright 2006 by Pearson Education 68 Assertion example 3 // pre : y >= 0, post: returns x^y public static int pow(int x, int y) { int prod = 1; // Point A while (y > 0) { // Point B if (y % 2 == 0) { // Point C x *= x; y /= 2; // Point D } else { // Point E prod *= x; y--; // Point F } // Point G } // Point H return prod; } y == 0y % 2 == 0 Point A Point B Point C Point D Point E Point F Point G Point H Which of the following assertions are true at which point(s) in the code? Choose ALWAYS, NEVER, or SOMETIMES. y == 0y % 2 == 0 Point A SOMETIMES Point B NEVERSOMETIMES Point C NEVERALWAYS Point D NEVERSOMETIMES Point E NEVER Point F SOMETIMESALWAYS Point G SOMETIMES Point H ALWAYS